Environmental considerations make it desirable to make use of electrically operated vehicles. Such vehicles include one or more electrical traction motors coupled to the motive or drive wheels of the vehicle. The traction motor(s) are provided with electrical energy from an electrical source, which is generally a storage battery, or bank of storage batteries. The electrical energy provided to a traction motor is controlled by an operator in such a manner as to provide the desired amount of acceleration. The traction motors are preferably alternating-current motors, rather than direct-current motors, because direct-voltage motors tend to have limited brush life, and high-speed operation is difficult because of commutator limitations. However, driving an alternating-current motor from a battery requires a dc-to-ac inverter, to convert the direct voltage of the storage battery to alternating voltage which can be used by the alternating-current motor.
When an alternating-current motor is used as a traction motor, its rotational speed .omega..sub.m depends upon the frequency of the alternating voltage applied thereto. Since the traction motor is mechanically coupled to a wheel, possibly by a gear arrangement, the speed of the motor must be varied in order to vary the speed of the vehicle. Varying the speed of the vehicle, then, imposes a requirement that the dc-to-ac inverter have a variable alternating output voltage, established by the operator's controls. It should be noted that, since frequency (f) and angular rate (.omega.) are related by a constant, they are used somewhat interchangeably herein, selecting that one which better fits the context.